Arthritis is a class of disease that affects 43 million Americans. The causes of arthritis are, in general, unknown. However, dysregulated inflammatory and immune responses apparently play very important roles in these diseases, since many types of arthritis involve chronic inflammation in different organs. Tumor necrosis factor alpha (TNFalpha) is a pro-inflammatory cytokine and plays an important role in the inflammatory processes of rheumatoid arthritis. Although TNFalpha is required for regulation of normal inflammatory and immune responses, acute elevated levels of TNFalpha may lead to septic shock during bacterial infection, while chronically elevated levels of TNFalpha are associated with the inflammatory processes of rheumatoid arthritis. Elevated levels of TNFalpha induce expression of many inflammatory genes. Expression of these genes is thought to elicit the swelling, pain and other effects of rheumatoid arthritis. Inhibition of TNFalpha function in vitro and in vivo has been shown to affect several animal models of inflammation. Modulation of TNFalpha levels has also been shown to reduce signs and symptoms of severely active rheumatoid arthritis patients. Thus, understanding the molecular mechanism of TNFalpha function will provide more therapeutic approaches for treatment of arthritic diseases. The present proposal seeks to apply molecular tools to elucidate the precise TNFalpha signaling pathway that leads to activation of NF-kB, a major transcription factor that controls the expression of various inflammatory genes. Specifically, we will investigate how RIP, a key signaling intermediate in the TNFalpha pathway, transmits TNFalpha signals to activate NF-kB. We will also examine how TNFalpha -induced signaling pathway is negatively regulated. Finally, we will use genetic complementation approaches to identify unknown signaling components that are required for TNFalpha -induced NF-kB activation. These studies will provide essential new information about the molecular mechanisms by which TNFalpha signals are transmitted to downstream components that activate the NF-kB family of transcription factors controlling expression of inflammatory genes.